1. Field of the Invention
This invention relates to a Si-doped gallium arsenide (GaAs) single crystal substrate made by using Vertical Bridgeman (VB) or Vertical Gradient Freeze (VGF), and more particularly to the Si-doped gallium arsenide (GaAs) single crystal substrate that is used as a substrate in fabricating an LED (Light Emitting Diode) or LD (Laser Diode).
2. Description of the Related Art
A compound semiconductor single crystal such as gallium arsenide (GaAs) used as a substrate is conventionally made by various industrial methods such as Horizontal Bridgeman (HB), Liquid Encapsulated Czochralski (LEC), Vertical Bridgeman (VB) and Vertical Gradient Freeze (VGF). For example, Japanese patent application laid-open No. 5-70276 discloses an apparatus for making a group III–V or II–VI compound semiconductor single crystal by using the methods.
Among the above methods, VB and VGF are promising methods for making a good crystal with a lower dislocation density at a lower cost than the other methods. The method of making GaAs single crystal by VB or VGF is conducted such that a seed crystal is disposed at the bottom of a crucible and a solid raw material is disposed over the seed crystal, then the upper part of the seed crystal is melt while melting all the solid raw material, then the raw-material melt is cooled such that it is gradually solidified from the vicinity of seed crystal to the upper side, thereby growing the single crystal.